Fig 1. Schematics of the bio-optical approach used to quantify the rate of photons absorbed in photosystem II.

First, the phytoplankton absorption spectrum (a(λ)) is normalized to the chl a concentration [a*(λ)]. Then, a*(λ) is weighted to the spectrum of the incubation light [E(λ)/E_PAR] to give the spectrally-weighted chl a-specific light absorption ($\overline{a}*$). Finally $\overline{a}*$ is corrected for the ratio of absorbed quanta in PSII (a*_PSII:a*) to yield the PSII-specific light absorption coefficient [$\overline{a}*$ _PSII, m² (mg chl a)⁻¹]. See text for details.